Various hybrid powertrain architectures are known for managing the input and output torques of various torque-generative devices in hybrid vehicles, most commonly internal combustion engines and electric machines. One such hybrid powertrain architecture comprises a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, typically an internal combustion engine, and an output member for delivering motive torque from the transmission to a driveline of the vehicle. First and second electrical machines are operatively connected to an electrical energy storage device for interchanging electrical power therebetween. The first and second electrical machines comprise motor/generators operable to transform the electrical power to motive torque for input to the transmission, independently of torque input from the internal combustion engine. The first and second electrical machines are further operable to transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy potential that is storable in the electrical energy storage device. A control unit is provided for regulating the electrical power interchange between the electrical energy storage device and the first and second electrical machines.
Engineers implementing powertrain systems including transmissions are tasked with developing gear shifting schemes. Such transmission systems typically include devices able to operate in one of a plurality of fixed-gear modes, wherein shifting between the fixed gears occurs in response to predetermined operating conditions, and often not involving an overt request for shift from a vehicle operator.
In fixed gear operation, the internal combustion engine operates by providing an input speed and torque to the transmission device. The transmission input speed is equal to transmission output speed multiplied by the initial fixed gear ratio. When a shift is commanded, torque is off-loaded from a currently applied clutch. When an oncoming clutch is applied, the transmission input speed, coming from the internal combustion engine, needs to match the transmission output speed multiplied by the oncoming gear ratio. When the input speed from the engine does not match the transmission output speed multiplied by the oncoming gear ratio, driveline jerks, clutch slippage, and other problems leading to customer dissatisfaction occur. Furthermore, such actions as driveline jerks and clutch slippage may affect operating temperatures of the transmission clutches, and therefore clutch durability. On a hybrid powertrain system having a plurality of torque-generative devices, there are additional variables and degrees of freedom affecting operation of the powertrain which must be considered and managed during shift operation.
Therefore, there is a need to for a method and apparatus to control powertrain operation during gear shifting events for a hybrid powertrain system, to address concerns mentioned hereinabove.